High speed steel broaches are a common cutting tool in many types of metal working applications.
The application of pre-sharpened disposable cutting inserts to broaches in general has been very limited. In the case of roughing the blade root forms in turbine wheel discs, it has been virtually non-existent. This invention is intended to address the application of pre-sharpened disposable cutting insert broaches to turbine wheel discs and other uses. It is further the intent of the invention to accomplish this in a most economical way, through initial low cost of the broach and its improved operating efficiency, by virtue of much lower machining times and lowered tool maintenance costs.
Standard positive rake indexable inserts usually allow only 5.degree.-8.degree. rakes. However, somewhat higher positive rakes are much more suited to the special metals used in turbine discs.
Few broaching operations require the deep slotting associated with turbine discs. This deep slotting necessitates a series of many broach holders, making the total broach assembly extremely long with lengths occasionally reaching 100 feet or more. This extreme length does not allow the luxury of providing one series of inserts for cutting the slot bottom and a separate series for the slot walls, as is the case with crank shaft pin diameter broaching. (Reference U.S. Pat. No. 4,740,115)